Two position low pitch stop



March 30, 1965 N. B. NEWTON TWO POSITION LOW PITCH STOP Filed Dec. 25, 1963 United States Patent Glifice 3,175,620 Patented Mar. 30, 1955 3,175,620 TWG POSITION LW PIT CH STOP Norman B. Newton, South Glastonbury, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Dec. 23, 1963, Ser. No. 332,507 3 Claims. (Cl. Uli-160.32)

This invention relates to variable pitch aeronautical propellers and particularly to a two positioned stop therefor.

It is customary to provide for aeronautical propellers a low pitch stop which prevents the propeller blades from going below a predetermined blade angle to assure safety in the ight of the aircraft. However, for partieular types of aircraft, particularly the short takeoff and landing operation (S.T.O.L.) it is desirable to go below this setting to a lower blade angle so as to achieve a higher drag to reduce air speed and maintain higher engine speed for reducing the time to achieve maximum power. This blade angle is slightly higher than the blade angle desired to place the propeller in the reversing operation. The reason for the second low pitch stop is to allow a last minute absortion of a landing on a short runway with maximum climb power available in the least possible time.

While the use of dual positional low pitch stops have been employed in the past, such systems customarily utilize two separate servo pistons for each of the stop positions. Accordingly, such a device is complicated inasmuch as dual servo devices and the attendent redundancy of component parts are necessary. l have found that I have been able to provide atwo positional low pitch stop with the utilization ofbut a single servo piston. Obviously, this results in a simplified system With the attendant advantages of a lower cost, simplified propeller construction and a reduction in weight and size of the overall propeller. These advantages obviously are of particular importance particularly in. View of the fact that weight and size of the aircraft components bear a direct relationship to the overall flight capabilities of the aircraft.

lt is, therefore, an object of this invention to provide for a propeller as described a two positioned low pitch stop system.

A still further object of this invention is to provide a two positional low pitch stop system which is actuated by a singleservo piston.

And a still further object of this invention is to obtain' the advantages enumerated hereinabove.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawing which illustrate an embodiment of the invention.

The single figure is a schematic illustration of a propeller and its control illustrating this invention.

This invention contemplates the modification of stop mechanism of the type disclosed in the Forman U.S. Patent Number 2,477,868 and the Lambeck U.S. Patent Number 2,843,212. Essentially, these patents show a low pitch stop'which is pivotally mounted Within the propeller and is adapted to engage the cam of the pitch changing mechanism 'to positively hold it in a xed pitch position. A hydraulically actuated servo motor controls the position of a wedge which holds the pivotally mounted low pitch stop mechanism in a desired position. In the` event that reversing is desired the servo piston is actuated by increasing the pressure acting on the servo piston for retracting the wedge. Thiscauses the` low pitch stop mechanism to retract and hence allows the pitch changing motor to move over the stop and rotate the blades to a reverse blade angle. When it is desired to move the propeller back into the normal operating range, pressure is relieved behind the low pitch servo motor and the spring acting on the Wedge returns the wedge back to its normal position and hence movesthe low pitch stop cam back to its engaging position. For details of a suitable pitch changing mechanism,` reference is hereby made to the aforementioned Forman patent and Lambeck patent.

Referring now to the drawing showing the propeller generally indicated by numeral 10 comprising hub 12 supporting a plurality of circumferentially mounted propeller blades 14` (only one of which is shown) adapted for variable pitch positioning. Mounted forward of the hub is propeller dome 16 which houses the pitch changing mechanism generally indicated by numeral 18 and the low pitch stop mechanism generally indicated by the numeral 20. Oil is supplied to both ends of the pitch changing motor for moving it relative to the dome. The pitch changing motor 18 cooperates with suitable camming mechanism for converting the longitudinal movement of the motor to rotary movement. A gear carried on one end of the cam mates with a gear mounted on the root of each of the propeller blades for rotating the blade about its ylongitudinal axis for varying its blade angle. For a more detailed description of the cam and the servo motor, reference may be made to Caldwell et al., U.S. Patent Number 2,174,717 or Martin et al., U.S. Patent Number 2,280,713.

The propeller may also contain a suitable pitch lock mechanism for preventing the pitch of `the blade from seeking a lower blade angle when in its engaged position.

Splinedring 21 is attached to the hub which spline isV intended to engage splines 22 suitably supported in the rotating gear of the pitch change motor. SplineV 22 is movable longitudinally and is urged toward spline 21 by springs 24 and is separated therefrom by virtue of the pressure in chamber 166 acting on the shoulder 26 formed on the rear end of the spline 22. The operation of the pitch lock will be more fully explained in the description to follow.

As is Well-known in the prior art, the governor serves to direct hydraulic iluid Ito the fore or aft end of the servo motor for positioning the propeller blades at the proper blade angle for maintaining constant propeller rotational Speed. This is generally shown iu the drawing where the governor, generally illustrated by numeral 28, receives pressurized fluid through line 3Q which is pressurized by pump 32 and directs* the fluid to either the high pitch line 34 or low pitch line 36 for leading pressurized fluid' When of the dome and through a plurality of passages 42 (only one of which being shown). This fluid' acts on the forward surface of servo `mot-or 18 to urge -it towardthe left in an increasing pitch direction.

Fluid from low pitch line 36 is directed to -act on thev opposite surface of servo motor 18 through branch line- 44 into chamber 46 and through the space provided be# tweenthe cam 48 and the inner diameter surface 50'of servo piston 17 and'eventually to chamber S2. This fluid acts in a direction to move the servo piston toward the right for effectuating a decrease in pitch movement.

When the propeller control calls for an increase in pitch,

it is therefore apparent that pressurized fluid is directed into line 34 to the Afore end of servo piston 17, namely chamber 38 while the iluid acting on the aft end, namely in chamber 52 is directed to the governor 28 through the various low pitch passages, noted above, and eventually dumping into the drain line 60 and back to reservoir 61. And conversely, when the propeller governor is requesting a .decrease in propeller pitch, pressurized fluid is directed to chamber 52 to act on the `aft end of servo piston 17 through the various passages noted above, while chamber 38 on the fore end of servo piston 17 is connected to drain via line 60. Since governors and their attending control mechanisms are well-known in the art, and for the sake of convenience, the detailed description thereof is eliminated from this description. However, for a more detailedv description of the governor and its control mechanism, reference may be made to the patents mentioned supra, as Ifor example the Caldwell et al., U.S. Patent Number 2,174,717 or Martin et al., U.S. Patent Number 2,280,713 or to Luiz et al., U.S. Patent Number 2,943,686.

The low pitch stop mechanism comprises rotary mounted low pitch stop cam 62 which extends radially so that the end of servo motor 17, when the servo motor slides over the stop mechanism,'engages the first shoulder 64. A second shoulder formed on Vthe cam axially spaced from the iirst shoulder engages servov piston 17 when in the second stop position. The stop is pivotally mounted at 68 and moves radially inward -upon releasing Wedge y70. Wedge 70 is retained in this position by virtue of spring 72.

VTo release the wedge and drop the -loW pitch stop cam 62, pressurized uid is admitted into chamber 74 and directed through the annular groove defined by the outside surface of tube 40 and the inner sur-face of sleeve 76 eventually into chamber 78 formed on the aft surface of servo piston `80 by way of passages 82 formed therein. This pressure acting on low pitch stop servo 80 causes both the tu-bular member 46 and sleeve to move toward the righ-t until shoulder 84 formed on sleeve 76 abuts against Wedge4 70 moving it slightly so that the notch 46 formed on the endof cam 62 engages the top surface of Wedge 7 0. The position of the cam or low pitch stop is in the second position at this point at say 2.

The pressure for controlling the movement of the low pitch stop servo piston is controlled by the control mechanism generallyindicatcd by numerals 86 and 88.

' Operation of low positional stops may best be understood by considering when the aircraft Vis making an approach for a landing. The pilot will rotate pilot lever 90 for rotating cam 92 which in turn depresses plunger 94 downwardly to unseat ball valveY 96. This has the elect of conducting low pitch pressure fluid through line 98 and into line 100 and into chamber 102 yfor urging valve member 104 in the closed position. Valve generally indicated by numeral 106 is the decrease pitch relief Valve which normally serves to dump low pitch pressure in line 36 to drain Via line 98, valve 106 and lines 108 and 1:10 when the value of the fluid goes above the spring force exerted by spring 112 together with the drain reference pressure acting behind valve element 104. This serves to develop the proper operational pressure in the low pitch control lines. With'the increase of pressure acting on the rear of valve element 104, the pressure in line 36 is al! -lowed to increase to a vaine above this normal operating pressure value. This fluid which is communicating with the liuid in line 44 is then directed to the ight'stop release valve generally indicated by numeral 114. Valve 1'14 comprises spool 116 having axially spaced lands 118 and 120. Spring 122 acting against land 120 constantly urges the valve in the position shown in the drawing. It may use as a reference pressure the low pressure in the system or drain pressure communicating thereto through lines 126 and 128 and 110.

From the foregoing, it is apparent that the pressure increased by -actuation of the decrease pressure relief` valve 1061's admitted to act against land 118 for urging The 4 valve toward the left. Obviously the governor at this time i-s direct-ing pressurized iluidto the 101W pitch side of the pitch changing motor causing the blades to rotate to the rst low pitch stop which may be, say 16 degrees. When spool 116 shifts to the left, it communicates pressurized iluid in the low pitch line 36 through line 130 which in turn directs ilu-id to the approach stop release valve generally indicated by numeral 132. This valve may comprise spool 134 having three axially spaced lands 136 and 138 and 140. Fluid issuing -from line 130 is directed firs-t -to annular chamber 142 through drill passage 144 formed in the casing of valve 132 to annular chamber 146 where in turn, it is directed to chamber 74 via :line 148. As was mentioned above, fluid from chamber 74 is directed to chamber 78 located behind servo piston 80 for moving the servo piston 80 to the right for withdrawing the wedge so that the blades may go through the iirst stop. Hence, pitch changing piston 17 will albut against shoulder 66 in the 'second stop position. Since servo piston S0 abut-s through shoulder 150 against the liange 152 formed on the end of sleeve 40, sleeve 46 will move with servo piston 80 until the end of sleeve 40 uncovers the opening @formed on the end `of passage 154. As soon as the opening is uncovered, fluid becomes metered out of chamber 78 and directed to dra-in pressure on the high pitch side of the servo piston 17 which drops the pressure in chamber 78 to just balance the force of return spring 190 at this metering position. This holds the low pitch stop servo piston in this position and spring 72 assures that the wedge remains against recess 86. While not absolutely necessary, the propeller may contain spring loaded stop 158 which serves to butt against theI outer side or servo piston 80 to assure that the piston remains in the proper position to hold the wedge against the notch 86.

When it is desired to move the blades in the reverse posit-ion, power lever 90 is rotated further for rotating cam 160 which in turn depresses plunger 162 for unseating ball valve 164. This serves to deactivate the pitch lock by directly subjecting chamber 166 to high pressure to assure that splines 21 and 22 do not engage. The pressure iiuid is directed to chamber 166 through lines 168, 169, 170, 171 and 30. Upon opening valve 164 high pressure iluid .bypassing the governor is admitted to act on the right end of spool `172 which urges the -spool against the force of spring 174 to the left, communicating line 170 with line 169. This has the eifect of overriding the pitch lock speed sensing mechanism generally indicated by numeral 176 which normally positions Valve 178 for directing high pressure to or relieving pressure from chamber 166 in order to actuate or deactivate the pitch lock mechanism as a `'func-tion of the rotational speed of the propeller. Y V

By shifting spool 172, it will be appreciated that the pressure passing through the pitch lock lines is higher than the normal operating pressure of the system which is normally regulated by valve 192. This pressure is admit-ted to valve 132 via line 169 to act against land urging it to the left against the force created by spring 180 and the reference drain pressure admitted behind spool 136 through line 182. When spool 1'34 shifts to the left, land 138 moves to block port 184 formed adjacent to line 154 and to connect port 186 yformed adjacent to line 148 with line 1-30. This blocks off the flow passing through line 154 and serves to increase the pressure in chamber 74 to still a higher value (supply pressure) for urging piston 80 to the right a still further distance for withdrawing wedge 70. It is apparent from the lforegoing that the inner surface formed on pitch changing motor 17 passes over the low pitch stop cam .allowing the propeller blades to move into the reverse position.

What has been shown by this invention is means `for obtaining a two positional stop by utilizing a single servo piston. Such a system is characterized as being relatively simple to construct, relatively inexpensive to manuar'faeao facture yet capable of rugged use, while eliminating the need of a second low pitch stop servo piston and its -attendant structure.

lt should be understood tha-t the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept.

I claim:

l. For an aeronautical propeller having variable pitch blades and means including a pitch change motor for varying the pitch of said blades, stop means adapted to engage said pitch change motor, to restrain the movement thereof providing a iirst stop preventing the pitch from going below a irst predetermined pitch and providing a second stop preventing the pitch from going below a second predetermined pitch, a source of pressurized fiuid and a drain, control means including fluid connecting means interconnecting said pitch change motor with said source and said drain for efectuating pitch change movement of said blades and adapted to position said motor against said stop means, normally inoperative pitch lock means including independent coordinating means for developing a pressure to render the pitch lock inoperative and releasing the pressure to allow said blades to loclc and be prevented from moving toward a low pitch, means for disengaging said stop means so that the motor will pass over said first stop so as to engage said second stop and then further disengage said stop means so that the motor will pass over said second stop whereby said blades will be positively restrained at said first predetermined pitch and then a second predetermined pitch and then allowed to go to a pitch beyond said second predetermined pitch, said means including a servo piston operatively connected to said stop means, a uid receiving chamber adjacent said servo piston receiving fluid from said source, means for regulating the Huid pressure in said chamber for ettectuating movement of said servo piston to disengage said stop means and additional means responsive to the pressure for rendering said pitch lock means inoperative for further regulating the pressure in said chamber for eftectuating further movement of said servo piston for further disengaging said stop means.

2. For a variable pitch propeller having a high pitch chamber, a low pitch chamber, a pitch change motor located therebetween and means for directing oil into and out of said high and low pitch chambers for moving said pitch change motor to vary the pitch, stop means adapted to engage said motor to prevent the pitch from going below a first predetermined pitch value and a second predetermined pitch value, said stop means comprising a retractable cam having a pair of spaced outwardly projecting abutments adapted to engage said pitch change motor and a pair of spaced inwardly extending recesses, moveable wedge means adapted to be received by said recesses, means including a servo piston having a uid receiving chamber mounted adjacent thereto operatively connected to said wedge means for moving it from one of said recesses to the other of said recesses for allowing said cam to retract and permitting said pitch change motor to pass over one of said abutments, iirst valve means interconnecting said low pitch chamber and said iluid receiving chamber for moving said servo piston to a first position and second valve means normally interconnecting said fluid receiving chamber and said high pitch chamber movable to disconnect said fluid receiving chamber and said high pitch chamber to move said servo piston to effectuate movement of said wedge means for allowing said cam to retract further to permit said pitch change motor to pass over said second abutment.

3. For an aeronautical propeller having variable pitch blades and means including a high pitch chamber, a low pitch chamber and a pitch change motor for varying the pitch of said blades, a dome mounted forward of said blades about the rotational axis of said propeller, a retractable cam in said dome having a iirst shoulder and a second shoulder spaced from said irst shoulder each extending laterally from said rotational axis and each adapted to engage said pitch change motor, a source of pressurized fluid and a drain, control means including tluid connecting means interconnecting said high pitch chamber and said low pitch chamber with said source and said drain for ettectuating pitch change movement of said blades and adapted to position said motor to abut against said lst and 2nd shoulders, normally inoperative pitch lock means including independent coordinating means for engaging said blades and preventing them to move toward a low pitch, means for allowing said cam to retract so that the pitch change motor will pass over said rst shoulder so as to engage said second shoulder and then to allow said cam to retract further so that the pitch change motor will pass over said second shoulder whereby said blades will be positively restrained at a rst predetermined blade angle and then a second predetermined blade angle and then allowed to go to a blade angle beyond said second predetermined blade angle, said means including a servo piston operatively connected to said cam, a uid receiving chamber adjacent said servo piston receiving fluid from said source, means for regulating the fluid pressure in said chamber for eiectuating movement of said servo piston to allow said cam to retract and additional means responsive to said pitch lock means for further regulating the pressure in said chamber for eectuating further movement of said servo piston for allowing said cam to retract further.

References Cited bythe Examiner UNITED STATES PATENTS 3,090,445 5/63 Fischer 170-l60.21 3,103,249 9/63 Hildebrandt et al. 170-160.32 3,143,175 8/64 Elmes et al. 170-l60.32

JULIUS E. WEST, Primary Examiner. 

3. FOR AN AERONAUTICAL PROPELLER HAVING VARIABLE PITCH BLADES AND MEANS INCLUDING A HIGH PITCH CHAMBER, A LOW PITCH CHAMBER AND A PITCH CHANGE MOTOR FOR VARYING THE PITCH OF SAID BLADES, A DOME MOUNTED FORWARD OF SAID BLADES ABOUT THE ROTATIONAL AXIS OF SAID PROPELLER, A RETRACTABLE CAM IN SAID DOME HAVING A FIRST SHOULDER AND A SECOND SHOULDER SPACED FROM SAID FIRST SHOULDER EACH EXTENDING LATERALLY FROM SAID LONGITUDINAL AXIS AND EACH ADAPTED TO ENGAGE SAID PITCH CHANGE MOTOR, A SOURCE OF PRESSURIZED FLUID AND A DRAIN, CONTROL MEANS INCLUDING FLUID CONNECTING MEANS INTERCONNECTING SAID HIGH PITCH CHAMBER AND SAID LOW PITCH CHAMBER WITH SAID SOURCE AND SAID DRAIN FOR EFFECTUATING PITCH CHANGE MOVEMENT OF SAID BLADES AND ADAPTED TO POSITION SAID MOTOR TO ABUT AGAINST SAID 1ST AND 2ND SHOULDERS, NORMALLY INOPERATIVE PITCH LOCK MEANS INCLUDING INDEPENDENT COORDINATING MEANS FOR ENGAGING SAID BLADES AND PREVENTING THEM TO MOVE TOWARD A LOW PITCH, MEANS FOR ALLOWING SAID CAM TO RETRACT SO THAT THE PITCH CHANGE MOTOR WILL PAS OVER SAID FIRST SHOULDER SO AS TO ENGAGE SAID SECOND SHOULDER AND THEN TO ALLOW SAID CAM TO RETRACT FURTHER SO THAT THE PITCH CHANGE MOTOR WILL PASS OVER SAID SECOND SHOULDER WHEREBY SAID BLADES WILL BE POSITIVELY RESTRAINED AT A FIRST PREDETERMINED BLADE ANGLE AND THEN A SECOND PREDETERMINED BLADE ANGLE AND THEN ALLOWED TO GO TO A BLADE ANGLED BEYOND SAID SECOND PREDETERMINED BLADE ANGLE, SAID MEANS INCLUDING A SERVO PISTON OPERATIVELY CONNECTED TO SAID CAM, A FLUID RECEIVING CHAMBER ADJACENT SAID SERVO PISTON RECEIVING FLUID FROM SAID SOURCE, MEANS FOR REGULATING THE FLUID PRESSURE IN SAID CHAMBER AFTER EFFECTUATING MOVEMENT OF SAID SERVO PISTON TO ALLOW SAID CAM TO RETRACT AND ADDITIONAL MEANS RESPONSIVE TO SAID PITCH LOCK MEANS FOR FURTHER REGULATING THE PRESURE IN SAID CHAMBER FOR EFFECTUATING FURTHER MOVEMENT OF SAID SERVO PISTON FOR ALLOWING SAID CAM TO RETRACT FURTHER. 